获取记录的当前用户电子邮件

Question

I am using firebase to do the authentication in my application, and everything works fine, but when i log in i want to display the user email that is logged in, and what i did crashes the application when i run it, so i did this:

 auth = FirebaseAuth.getInstance();
  userTxt.setText(auth.getCurrentUser().getEmail().toString());

i defined a auth object and then used that auth to get the current user email, after that all in one line i passed that to my textView, what am i doing wrong here?

StackTrace

04-09 09:00:11.247 2987-2987/com.esmad.pdm.friendlymanager E/AndroidRuntime: FATAL EXCEPTION: main
                                                                             Process: com.esmad.pdm.friendlymanager, PID: 2987
                                                                             java.lang.RuntimeException: Unable to start activity ComponentInfo{com.esmad.pdm.friendlymanager/com.esmad.pdm.friendlymanager.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.auth.FirebaseUser com.google.firebase.auth.FirebaseAuth.getCurrentUser()' on a null object reference
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
                                                                                 at android.app.ActivityThread.access$800(ActivityThread.java:151)
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:102)
                                                                                 at android.os.Looper.loop(Looper.java:135)
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5254)
                                                                                 at java.lang.reflect.Method.invoke(Native Method)
                                                                                 at java.lang.reflect.Method.invoke(Method.java:372)
                                                                                 at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
                                                                                 at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
                                                                              Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.auth.FirebaseUser com.google.firebase.auth.FirebaseAuth.getCurrentUser()' on a null object reference
                                                                                 at com.esmad.pdm.friendlymanager.MainActivity.onCreate(MainActivity.java:34)
                                                                                 at android.app.Activity.performCreate(Activity.java:5990)
                                                                                 at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
                                                                                 at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
                                                                                 at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) 
                                                                                 at android.app.ActivityThread.access$800(ActivityThread.java:151) 
                                                                                 at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) 
                                                                                 at android.os.Handler.dispatchMessage(Handler.java:102) 
                                                                                 at android.os.Looper.loop(Looper.java:135) 
                                                                                 at android.app.ActivityThread.main(ActivityThread.java:5254) 
                                                                                 at java.lang.reflect.Method.invoke(Native Method) 
                                                                                 at java.lang.reflect.Method.invoke(Method.java:372) 

Answer 1

it crash because getCurrentUser() might return null

try this

    mAuth = FirebaseAuth.getInstance();
    final FirebaseUser theUser = mAuth.getCurrentUser();
    if (theUser !=null)
    String _UID = theUser.getEmail().toString();

and I prefer to use AuthStateListener

In MainActivity

    private FirebaseAuth mAuth;
    private FirebaseAuth.AuthStateListener mAuthListener;

then in onCreate

mAuthListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                FirebaseUser user = firebaseAuth.getCurrentUser();
                if (user != null) {
                    // User is signed in
                    String _UID = Theuser.getUid();
                    String Uemail= Theuser..getEmail().toString();
                } else {
                    // User is signed out
                }
            }
        };

and in onStart

@Override
public void onStart() {
    super.onStart();
      mAuth.addAuthStateListener(mAuthListener);
}

and in onStop

@Override
public void onStop() {
    super.onStop();
    if (mAuthListener != null) {
        mAuth.removeAuthStateListener(mAuthListener);
    }
}

Answer 2

Your logcat is giving you the answer:

Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'com.google.firebase.auth.FirebaseUser com.google.firebase.auth.FirebaseAuth.getCurrentUser()' on a null object reference

so your invoking getCurrentUser() on a null object.

extra:

I have just come upon another situation where the user's email would return null even if you have correctly initialized your FirebaseUser

There's a closed bug report already filed with google:

When you go to the Auth > Sign-In Methods page of your project in the Firebase console. do you have One account per email address on or off? If you allow multiple accounts per email address, you will get null for FirebaseUser. getEmail()

You have to use the option: "Prevent creation of multiple accounts with the same email address" or else FirebaseUser.getEmail() will return null

Ps: only users who first logged in after the option was turned off will be able to use this method successfully